Method for producing silica aerogel blanket and apparatus for producing same

ABSTRACT

The present invention relates to a method for producing a silica aerogel blanket and an apparatus for producing the same, which are capable of easily controlling the physical properties of a silica aerogel blanket by separately injecting silica sol and a gelation catalyst to control gelation time, improving aerogel pore structure to be uniform and improving thermal insulation performance by sufficiently and uniformly impregnating the silica and the gelation catalyst into a blanket, reducing the loss of silica sol and gelation catalyst by allowing the silica sol and the gelation catalyst to pass on an ascending slope before gelation to remove any excessive silica sol and gelation catalyst exceeding an appropriate impregnation amount, and providing a silica aerogel blanket having less process trouble, and less dust.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2017-0107467, filed on Aug. 24, 2017, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

The present invention relates to a method for producing a silica aerogelblanket and an apparatus for producing the same.

BACKGROUND ART

Aerogel is a superporous, high specific surface area (≥≥500 m²/g)material having a porosity of about 90-99.9% and a pore size in therange of 1-100 nm, and is a material excellent in ultra-light weight,super thermal insulation, ultra-low dielectric, and the like.Accordingly, research on the development of aerogel materials as well asresearch on the practical use thereof as transparent insulationmaterials, environmentally friendly high temperature insulationmaterials, ultra-low dielectric thin films for highly integrateddevices, catalysts and catalyst carriers, electrodes forsuper-capacitors, and electrode materials for seawater desalination havebeen actively studied.

The biggest advantage of aerogel is that aerogel has a super-insulationexhibiting a thermal conductivity of 0.03 W/mK or less, which is lowerthan that of an organic insulation material such as conventionalStyrofoam, and that fire vulnerability and the occurrence of harmfulgases in case of fire which are fatal weaknesses of the organicinsulation material can be solved.

In a typical method for producing a silica aerogel-containing blanket, asolution obtained by mixing a silica precursor sol and a gelationcatalyst in a gel casting process is impregnated into a fiber to producea silica aerogel-containing blanket. Therefore, there are disadvantagesin that when the silica precursor sol and the gelation catalyst aremixed, a sol-gel chemical reaction immediately starts and the viscosityof the mixed solution is increased allowing particles to form beforesufficient impregnation into the fiber is achieved, so that it isdifficult to control the gelation rate, and the gelled aerogel isdamaged or lost during a process, so that the insulation performance ofa final product is deteriorated.

In addition, when the precursor sol and the gelation catalyst areinjected onto a moving element as in a Roll-to-Roll process, theprecursor sol and the gelation catalyst are not sufficiently impregnatedinto a fibrous blanket located on the moving element, allowing unevenimpregnation to occur on the surface of the blanket, therebydeteriorating the insulation performance thereof. When an injectionamount of the precursor sol and the gelation catalyst is increased inorder to prevent such a problem, the amount that can be impregnated intothe fibrous blanket is exceeded, and the precursor sol and gelationcatalyst exceeding the impregnation amount may overflow from the movingelement, resulting in process loss. Furthermore, a solid, such aspowder, is formed due to a subsequent gelation of the overflown mixture,which causes a problem of acting as a process trouble factor for amechanically operating processing device.

Therefore, the inventors of the present invention have developed thepresent invention after conducting studies in order to solve suchtypical problems.

PRIOR ART DOCUMENT

-   (Patent Document 1) U.S. Pat. No. 9,476,123 B2 (Oct. 25, 2016)

DISCLOSURE OF THE INVENTION Technical Problem

An aspect of the present invention provides a production method capableof producing a silica aerogel blanket having a uniform pore structureand uniform and excellent thermal insulation performance by uniformlyimpregnating silica sol and a gelation catalyst into a fibrous blanketand controlling the injection rate of the silica sol and the gelationcatalyst.

Another aspect of the present invention provides a production methodcapable of reducing the loss of silica sol and gelation catalyst,reducing process trouble, reducing dust, and furthermore, maximizingoperation stability through managing solvent vapor and maximizingeconomic feasibility through reducing solvent loss.

Another aspect of the present invention provides an apparatus forproducing a silica aerogel blanket capable of producing the silicaaerogel blanket.

Technical Solution

According to an aspect of the present invention, provided is a methodfor producing a silica aerogel blanket, the method including 1)separately injecting silica sol and a gelation catalyst into animpregnation tank in which a blanket is present;

2) impregnating the blanket with the silica sol and the gelationcatalyst separately injected into the impregnation tank;

3) transferring the blanket impregnated with the silica sol and thegelation catalyst to a moving element through an ascending slope; and

4) gelling the impregnated blanket on the moving element.

According to another aspect of the present invention, provided is anapparatus for producing a silica aerogel blanket, the apparatuscomprising: an impregnation tank in which a blanket is impregnated withsilica sol and a gelation catalyst;

a blanket supply apparatus connected to one side of the impregnationtank and supplying a blanket;

a silica sol injection apparatus for injecting silica sol into theimpregnation tank such that the supplied blanket is impregnated with thesilica sol;

a gelation catalyst injection apparatus for injecting a gelationcatalyst into the impregnation tank such that the supplied blanket isimpregnated with the gelling catalyst;

an ascending slope connected to the other side of the impregnation tankand transferring the blanket impregnated with the silica sol and thegelation catalyst from the impregnation tank to a moving element; and

a moving element connected to the ascending slope and on which theblanket impregnated with the silica sol and the gelation catalyst isgelled.

Advantageous Effects

A method for continuously producing a silica aerogel blanket and anapparatus for producing the same according to the present invention arecapable of easily controlling the physical properties of a silicaaerogel blanket by controlling gelation time, producing a silica aerogelblanket having a uniform aerogel pore structure and uniform andexcellent thermal insulation performance, and reducing the loss ofsilica sol, gelation catalyst, and solvent during processing, therebyhaving an effect of reducing production costs, process trouble, and thegeneration of dust.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings attached herein illustrate preferred embodimentsof the present invention by example, and serve to enable technicalconcepts of the present invention to be further understood together withdetailed description of the invention given below, and therefore thepresent invention should not be interpreted only with matters in suchdrawings.

FIG. 1 is a schematic view showing a method for producing a silicaaerogel blanket according to an embodiment of the present invention.

FIG. 2 is a stereoscopic view showing an apparatus for producing asilica aerogel blanket according to an embodiment of the presentinvention.

FIG. 3 is a detailed view showing in detail silica sol and gelationcatalyst injection apparatuses and an impregnation tank of an apparatusfor producing a silica aerogel blanket according to an embodiment of thepresent invention.

FIG. 4 is a SEM photograph (scale=(a) 100 um, (b) 200 nm) of a silicaaerogel blanket prepared according to Example and Comparative Example ofthe present invention.

FIG. 5 is a thermal imaging camera photograph of a silica aerogelblanket prepared according to Example and Comparative Example of thepresent invention.

FIG. 6 is a graph showing the pore size distribution of a silica aerogelblanket prepared according to Example and Comparative Example of thepresent invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail tofacilitate understanding of the present invention. In this case, it willbe understood that words or terms used in the specification and claimsshall not be interpreted as having the meaning defined in commonly useddictionaries. It will be further understood that the words or termsshould be interpreted as having a meaning that is consistent with theirmeaning in the context of the relevant art and the technical idea of theinvention, based on the principle that an inventor may properly definethe meaning of the words or terms to best explain the invention.

The purpose of the present invention is to provide a method forproducing a silica aerogel blanket and an apparatus for producing thesame to solve problems of typical methods and apparatuses for producinga silica aerogel blanket, the problems such as the deterioration inthermal insulation performance due to uneven impregnation, the increasein raw material costs caused by the loss of raw materials such as silicasol and a gelation catalyst during processing, and the occurrence ofprocess trouble and generation of dust in processing equipment due togelation of an overflown solution of silica sol and a gelation catalyst.

Method for Producing Silica Aerogel Blanket

Specifically, as shown in FIG. 1 , a method for producing a silicaaerogel blanket of the present invention includes a method for producinga silica aerogel blanket, the method including 1) separately injectingsilica sol and a gelation catalyst into an impregnation tank in which ablanket is present;

2) impregnating the blanket with the silica sol and the gelationcatalyst separately injected into the impregnation tank;

3) transferring the blanket impregnated with the silica sol and thegelation catalyst to a moving element through an ascending slope; and

4) gelling the impregnated blanket on the moving element.

Hereinafter, a method for producing a silica aerogel blanket of thepresent invention will be described in more detail by each step.

Step 1)

The Step 1) of the present invention is characterized by separatelyinjecting silica sol and a gelation catalyst into a blanket supplied bya blanket supply apparatus.

In a typical production method, a silica aerogel blanket is produced byimpregnating a blanket with a mixed solution of silica sol and agelation catalyst in a gel casting step. However, in this case, when theprecursor sol and the gelation catalyst are mixed, a gelation reactionimmediately starts and the viscosity of the mixed solution is increased,thereby allowing particles to form before sufficient impregnation intothe fibrous fiber is achieved, so that it is difficult to control thegelation rate.

In addition, as a result, there arises problems in that the thickness ofthe silica aerogel blanket is not uniform, the gelled aerogel is damagedor lost during the transfer of the fibrous fiber or during processing,so that the insulation performance of a final product is deteriorated.Also, there arises problems in that aerogel particles are separated whenthe blanket is processed, such as cutting the blanket or bending thesame, so that dust is generated and the durability of the blanket isdeteriorated.

Accordingly, the present invention is characterized by separatelyinjecting silica sol and a gelation catalyst by using a separateinjection apparatus such that a gelation reaction occurs aftersufficient impregnation into a blanket is achieved.

As in the production method of the present invention, when silica soland a gelation catalyst are stored in a separate tank and are separatelyinjected through a separate injection apparatus, the injection rate ofeach of the silica sol and the gelation catalyst is controllable througha separate control unit thereof, so that there is an effect in that itis possible to produce a silica aerogel blanket having desired physicalproperties according to the control of gelation time.

Meanwhile, according to an embodiment of the present invention, thesilica sol and the gelation catalyst can be separately injected byvarious methods. The silica sol and the gelation catalyst can beinjected to the top or bottom of the impregnation tank to which theblanket is supplied.

Specifically, the silica sol can be injected from the bottom of theimpregnation tank, and the gelation catalyst can be injected from thetop of the impregnation tank, separately. Alternatively, the silica solcan be injected from the top of the impregnation tank, and the gelationcatalyst can be injected from the bottom of the impregnation tank,separately.

In this case, when compared with a case in which the silica sol and thegelation catalyst are injected in the same direction, the silica sol andthe gelation catalyst may not be completely mixed. However, theimpregnation of the silica sol and the gelation catalyst into the insideof the blanket can be complemented by a squeeze roller included in theimpregnation tank, and since the silica sol and the gelation catalystare mixed at the time of being impregnated into the blanket, it ispossible to prevent viscosity increase before the impregnation and moreprecisely control physical properties according to the control ofgelation time.

In addition, the silica sol and the gelation catalyst can be separatelyinjected from the top of the impregnation tank. In this case, added withthe pressurization by gravity, sufficient impregnation is ensured to theinner central portion of the blanket compared with the case in which thesilica sol and the gelation catalyst are separately injected from thebottom of the impregnation tank, and compared with the case in which thesilica sol and the gelation catalyst are separately injected from adifferent direction, a sufficient mixture is achieved to perform auniform gelation reaction.

Meanwhile, the present invention is characterized in that silica sol anda gelation catalyst are separately injected, and thus is characterizedin that gelation time and physical properties can be easily controlledby adjusting the injection direction, type, number, injection rate,distance between injection devices or from a blanket, and the like ofthe silica sol and the gelation catalyst.

According to an embodiment of the present invention, a precursor usablefor the silica sol of the present invention can be an alkoxide-basedcompound containing silicon, specifically, a tetraalkyl silicate such astetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS),methyl triethyl orthosilicate, dimethyl diethyl orthosilicatetetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutylorthosilicate, tetra secondary butyl orthosilicate, tetra tertiary butylorthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate,and tetradodecyl orthosilicate. Among these, the silica precursor of thepresent invention can be, more specifically, tetramethyl orthosilicate(TMOS), tetraethyl orthosilicate (TEOS), or a mixture thereof.

As the gelation catalyst of the present invention, a base catalyst canbe used, and the base catalyst serves to promote the gelation byincreasing the pH of the silica sol.

The basic catalyst can be an inorganic base such as sodium hydroxide andpotassium hydroxide; or an organic base such as ammonium hydroxide.However, in the case of an inorganic base, a metal ion included in acompound can be coordinated to a Si—OH compound. Thus, an organic basecan be preferred. Specifically, the organic base can be ammoniumhydroxide (NH₄OH), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropyl-ammonium hydroxide (TPAH),tetrabutylammonium hydroxide (TBAH), methylamine, ethylamine,isopropylamine, mono-isopropylamine, diethylamine, diisopropylamine,dibutylamine, trimethylamine, triethylamine, tri isopropylamine,tributylamine, choline, monoethanolamine, diethanolamine,2-aminoethanol, 2-(ethylamino) ethanol, 2-(methylamino) ethanol,N-methyldiethanolamine, dimethyl aminoethanol, diethylamino-ethanol,nitrilotriethanol, 2-(2-aminoethoxy)ethanol, 1-amino-2-propanol,triethanolamine, monopropanolamine, or dibutanol, and any one or amixture of two or more thereof can be used. More specifically, the baseof the present invention can be ammonium hydroxide (NH₄OH).

The base catalyst can be injected in an amount such that the pH of thesilica sol is 4 to 8. When the pH of the silica sol is out of the aboverange, the gelation is not easily obtained, or the gelation rate is tooslow, thereby deteriorating the processibility. In addition, since thebase can be precipitated when injected in a solid phase, it can bepreferable to be added in the form of a solution diluted with thealcohol (polar organic solvent).

Meanwhile, the silica sol and the gelation catalyst can be a solutioncontaining a polar organic solvent, and a solvent which can be used inthe present invention can be an alcohol having 1 to 6 carbon atoms,specifically ethanol.

In addition, a blanket base which can be used in the present inventioncan be a film, a sheet, a net, a fiber, a porous body, a foam, anon-woven body, a glass fiber, a glass fiber mat, or a laminate of twoor more layers thereof. In addition, according to the use, surfaceroughness can be formed or patterned on the surface thereof. Morespecifically, the blanket base can be a fiber capable of furtherimproving the thermal insulation performance by including a space or avoid through which silica aerogel can be easily inserted into theblanket base. Also, the blanket base can preferably have low thermalconductivity.

Specifically, the blanket base can be polyamide, polybenzimidazole,polyaramid, an acryl resin, a phenol resin, polyester,polyetheretherketone (PEEK), polyolefin (for example, polyethylene,polypropylene, or a copolymer thereof, and the like), cellulose, carbon,cotton, wool, hemp, a non-woven fabric, a glass fiber, or ceramic wool.More specifically, the blanket base can include a glass fiber orpolyethylene.

Step 2)

The Step 2) of the present invention is characterized by impregnatingthe blanket with the silica sol and the gelation catalyst separatelyinjected into the impregnation tank.

In a typical production method, silica sol and a gelation catalyst areinjected on a moving element as in a Roll-to-Roll process, so that it isdifficult to achieve sufficient impregnation into a fibrous blanket onthe moving element. Thereby, non-uniform impregnation occurs on thesurface of the blanket, and as a result, there is a problem in that theinsulation performance of a produced blanket containing aerogel isdeteriorated.

In addition, when an injection amount of the silica sol and the gelationcatalyst is increased in order to prevent such a problem, the amountthat can be impregnated into the fibrous blanket is exceeded, and thesilica sol and gelation catalyst exceeding the impregnation amount mayoverflow from the moving element, resulting in process loss.Furthermore, a solid, such as powder, is formed due to a subsequentgelation of the overflown mixture, which causes a problem of acting as aprocess trouble factor for a mechanically operating processing device.

Therefore, in order to ensure that the sufficient impregnation of silicasol and a gelation catalyst into a blanket is achieved, in the presentinvention, the silica sol and the gelation catalyst are injected into animpregnation tank to ensure that the sufficient impregnation is achievedin the impregnation tank.

The present invention is characterized in that silica sol and a gelationcatalyst can be separately injected in various manners as describedabove, and at the same time, is characterized in that the separateinjection is performed in an impregnation tank. When separately injectedon a moving element, silica sol and a gelation catalyst which have notyet mixed with each other to be subjected to gelation have a lowviscosity, thereby overflowing from the moving element, resulting in theloss of raw materials. Therefore, the present invention attempts tosolve the problem by separately injecting silica sol and a gelationcatalyst on to a blanket present in an impregnation tank. In this case,when compared with a case in which silica sol and a gelation catalystare separately injected on a moving element, the loss of raw materialsare significantly reduced, thereby significantly reducing raw materialcosts.

Meanwhile, in this case, the injected rate and the like can becontrolled to maintain the liquid level of the silica sol and thegelation catalyst in the impregnation tank of the present invention tooverflow a little over the fibrous blanket, so that it is possible tosecure uniform and excellent thermal insulation performance due touniform impregnation.

According to an embodiment of the present invention, the residence timeof a blanket the impregnation tank is 0.01 to 30 minutes, specifically0.5 to 10 minutes, more specifically 0.1 to 5 minutes. In order to allowthe blanket to stay in the impregnation tank for a period of time in theabove range, the supply speed of a blanket supply apparatus can beappropriately adjusted.

When the blanket stays in the impregnation tank longer than the aboveperiod of time, processing time is increased so that productivity isdecreased, or since a gelation reaction is performed starting from theimpregnation tank, gelation of more than an impregnation amount occurs,resulting in the loss of silica sol and gelation catalyst. Furthermore,a solid, such as powder, is formed due to a subsequent gelation of amixed solution without a blanket present on the impregnated blanket,which can become a process trouble factor for a mechanically operatingprocessing device. When the blanket stays in the impregnation tank lessthan the above period of time, sufficient impregnation may not beachieved.

Step 3)

The Step 3) of the present invention is characterized by transferringthe blanket impregnated with the silica sol and the gelation catalystfrom the impregnation tank to a moving element through an ascendingslope.

In a typical method, silica sol and a gelation catalyst present morethan an impregnation amount exceeding the amount that can be impregnatedon a fibrous blanket overflows from a moving element, resulting inprocess loss, so that economic feasibility is not good due to theincrease in raw material costs.

In addition, gelled sol that has not been impregnated into the blanketand remaining on the impregnated blanket without a fibrous structureforms aerogel due to a subsequent gelation process. However, since thereis no structural support, the aerogel is mechanically weak and separatedfrom the blanket in a solid phase such as powder. The separated solidphase in a power form acts as a trouble factor, blocking lines andhindering pump operations in subsequent processes (aging, surfacemodification, and drying), and specifically, poses a danger in asupercritical drying process using high pressure processes. In addition,such powder acts as a major cause of dust generated in a processingprocess of an aerogel blanket product, making processibility andworkability poor.

Therefore, in the production method of the present invention, a blanketimpregnated with silica sol and a gelation catalyst is transferred to amoving element through an ascending slope in an impregnation tank, sothat an excessive amount of a mixed solution of the silica sol and thegelation catalyst flows down along the slope into the impregnation tankto prevent excessive impregnation, ensuring an appropriate level ofimpregnation (saturated impregnation). As a result, the durability andthe thermal insulation of a product are improved, the loss of silica soland a gelation catalyst which are raw materials is reduced, the numberof emergency stopping is reduced, and the generation of dust is reduced,thereby solving typical problems.

In this case, as gravity is used, there is an advantage in that there isno separate energy supplied. To this end, it is necessary that themoving element of the present invention is located above theimpregnation tank.

In addition, according to an embodiment of the present invention, theangle of the ascending slope is greater than 0° to less than 180°,preferably great than 1° to less than 90°, more preferably greater than30° to less than 60° based on the bottom of the impregnation tank. Inorder to prevent excessive impregnation and to ensure an appropriatelevel of impregnation (saturated impregnation), it is necessary tomaintain an appropriate angle of the ascending slope. When the angle ofthe ascending slope is less than the above range, the effects ofpreventing excessive impregnation and reducing the loss of raw materialsmay be insignificant. When the angle of the ascending slope is greaterthan the above range, the movement angle of the blanket is large so thatthe blanket is damaged or the workability of the blanket isdeteriorated.

Step 4)

The Step 4) of the present invention is characterized by gelling theimpregnated blanket on the moving element to produce a silica wet gelblanket.

In the present invention, sufficient impregnation is achieved in theimpregnation tank, and a gelation reaction is performed after the silicasol and the gelation catalyst exceeding an appropriate impregnationamount is removed through the ascending slop, so that there is an effectof producing a silica aerogel blanket having desired physical propertiesby precisely controlling the gelation time according to the rate,temperature and length of the moving element.

Meanwhile, a blanket impregnated with silica sol and a gelation catalystcan be subjected to a gelation reaction while ascending on an ascendingslope. However, the effect of the ascending slope is not reduced becausethe gelation reaction is performed on the ascending slope, rather, therecan be the effect of the ascending slope is not reduced. Rather, therecan be an effect of shortening the gelation time.

The gelation reaction can be one forming a network structure from asilica precursor material, and the network structure can be a planarmesh structure in which specific polygons having one or more types ofatomic arrangement are linked to each other, or a structure in whichspecific polyhedrons share the vertices, edges, faces, and the likethereof with each other to form a three dimensional skeleton structure.

In addition, the purpose of the present invention is not only to reducethe loss of silica sol and a gelation catalyst, but also to enablesolvent vapor management without deteriorating the quality of a finalproduct or increasing gelation time.

Pores of silica gel are typically filled with a solvent derived from asolvent in which a silica gel precursor is polymerized. In general, apreferred solvent is a low molecular weight organic compound such as analcohol having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms.Other solvents which can be used include ethyl acetoacetate, acetone,dichloromethane, ether, and the like, but are not limited thereto.

However, due to a relatively high vapor pressure of a solvent (typicallyat room temperature), a considerable amount of solvent is evaporated,thereby causing various problems, such as solvent vapor release into theenvironment, exposure of workers to a highly concentrated solvent, firerisk due to highly concentrated flammable solvent vapor, overall lowprocess efficiency and increased operation costs.

Specifically, liquid, in the present invention, the lowest temperatureat which a solvent emits vapor having a concentration enough to form anignitable mixture with air near a liquid surface is referred to as a“flash point.” The temperature of most of the solvents at roomtemperature is above the flash point. For example, the flash point ofethanol and methanol at normal pressure is about 13° C. and about 11°C., respectively. Therefore, additional safety measures are required forgels prepared using such media. Such problems may be more problematic,for example, in a large-scale production facility in which a largeaerogel blanket is produced in an open environment. For example, asilica wet gel blanket having a thickness of 1 mm or greater and anexposed surface area of several square feet can emit a large amount ofsolvent.

When 1) casting thicker gel, 2) casting gel with a large exposed surfaceor a large casting area, or 3) both, more or more highly concentratedsolvent is expected to evaporate. Therefore, the present invention isapplied to a blanket having a thickness of at least about 0.5 mm, 1 mm,and 2 mm or more, which is in contrast to a gel film which typically hasa thickness in the micron range.

In general, a reduction in solvent vapor concentration can be achievedthrough 1) cooling a liquid solvent (that is, a solvent vapor supplysource), 2) diluting solvent vapor with another gas (for example, N2,argon, and the like), 3) air flow (for example, an exhaust fan) thatdelivers solvent vapor away from a solvent, or 4) a combination thereof.In addition, optionally, a casting apparatus or at least a portionthereof can be sealed to assist in solvent vapor management. In anembodiment of the present invention, the solvent vapor concentration canpreferably be lower than the solvent vapor concentration of the flashpoint.

Therefore, the present invention can provide a method for producing asilica aerogel blanket, the method capable of improving operationstability and reducing the loss of solvent by reducing solvent vaporconcentration near formed silica gel through solve vapor management,thereby increasing economic feasibility.

More specifically, gel is formed at a point in which a mixturecontaining a precursor exhibits resistance to flow and/or at the pointin which a continuous polymer network is formed throughout the volume ofthe mixture. The reaction rate associated with the gel formation cangreatly vary depending on factors such as reaction mechanism,concentration/chemical identity of components, and reaction conditions.In practice, without any limitation, a sol-gel reaction to form a gelmaterial is considerably slowed down at low temperatures. In otherwords, gelation time is generally increased at low temperatures. For aparticular production method, such as one including continuous gelproduction, a slow process may not be desirable since larger castingdevices, more catalysts, and the like are required. In an embodiment ofthe present invention, solvent vapor concentration is reduced after agel material is formed.

In an embodiment of the present invention, the present invention uses agel casting method for a continuous or semi-continuous gel preparationmethod in which the formed gel is cooled. At lower temperatures, thevapor pressure of the solvent in the wet gel (silica gel blanket) issignificantly reduced, enabling a more economical process and a saferworking environment. Such economic benefit may be more pronounced whensolvent recycling is required when considering other steps for recyclingsolvent vapor. Particularly at low temperatures, that is, below theflash point of the solvent, the combustion probability is greatlyreduced and the safety of process operators is improved. Accordingly, inan embodiment of the present invention, a step of dispensing a gelprecursor mixture at a predetermined rate such that the gel precursormixture is gelled to form a silica wet gel blanket; and a step ofcooling the prepared gel so as to reduce a solvent evaporation rate.

In order to cool the formed silica gel, cooling systems can be disposedon one side or multiple sides of the formed silica wet gel blanket.Optionally, a cooling system can be disposed by bypassing the silica wetgel composite.

Specifically, the cooling system can cool the formed silica wet gelcomposite through any of 1) cooling the silica wet gel compositedirectly, 2) cooling the silica wet gel composite through a movingelement, 3) cooling both the moving element and the silica wet gelcomposite, 4) cooling a precursor and a gelling catalyst respectivelybefore injecting the same, or 5) cooling an impregnation tank, or amixture in the impregnation tank.

In the present invention, the definition of the cooling is a decrease inthe temperature of a solvent in gel. In an embodiment of the presentinvention, the silica wet gel blanket is cooled to a temperature belowroom temperature, below about 20° C., or from about 0° C. to about 20°C., including all individual values within the range.

The cooling system can be shaped to be suitable to receive a movingelement while being sufficiently close to reduce the temperature of thesilica wet gel blanket. The cooling can be performed by any heattransfer mechanism, such as conduction, convection, radiation, or acombination thereof. Preferably, the cooling system preferably aims totarget only a region in which the silica wet gel blanket is formed.

In an embodiment of the present invention, as far as the design isconcerned, the cooling system can be implemented in any form as long asit is capable of achieving the temperature of the range described above.The cooling system can be a container designed to receive a desiredvolume of coolant fluid, and the fluid can flow through the container orbe fixed therein. In addition, optionally, the cooling system can becoupled to a slab, a housing, or a set of flow lines carrying a coolant.The flow line can be configured in a manner to cool a slab. In anembodiment, a simple winding pattern is used. In another form of thecooling system, gas stream can be delivered at a reduced temperature.

The method for producing a silica aerogel blanket of the presentinvention for solvent vapor management can be characterized in that

the silica sol and the gelation catalyst are continuously injected at afirst temperature at a predetermined rate sufficient to be gelled toproduce a silica wet gel blanket having a thickness of at least 0.5 mm,

the silica wet gel blanket is cooled at a second temperature on a movingelement by a cooling system with non-physical contact, and

the second temperature is lower than the first temperature.

In addition, as an embodiment, the method for producing a silica aerogelblanket of the present invention is characterized in that

the silica sol and the gelation catalyst are continuously injected at afirst temperature at a predetermined rate sufficient to be gelled toproduce a silica wet gel blanket having a thickness of at least 0.5 mm,

at least one side of the silica wet gel blanket is cooled at a secondtemperature, which is lower than the first temperature, on a movingelement by a cooling system with non-physical contact, and

at least the other side of the silica wet gel blanket composite iscooled at a third temperature, which is lower than the firsttemperature, on a moving element by a cooling system with non-physicalcontact.

As another embodiment, the method for producing a silica aerogel blanketof the present invention can characterized in that

the silica sol and the gelation catalyst are continuously injected at afirst temperature at a predetermined rate sufficient to the gelled toproduce a silica wet gel blanket having a thickness of at least 0.5 mm,

at least both sides of the silica wet gel blanket is cooled at a secondtemperature, which is lower than the first temperature, on a movingelement by a cooling system with non-physical contact.

Specifically, the second temperature can be 20° C. or less, morespecifically 0° C. to 20° C. In addition, a cooling medium used in thecooling system can be a fluid, a gas, or a mixture thereof.

Thereafter, the silica wet gel blanket of the present invention may begel blanket may be recovered in the form of a roll and further besubjected to aging, surface modification, and drying.

The aging is a process in which the silica wet gel composite is left atan appropriate temperature such that the chemical change thereof can becompletely achieved. The aging can be performed by leaving the silicawet gel composite at a temperature of 50-90° C. for 1 to 10 hours in asolution in which a basic catalyst such as ammonia is diluted in anorganic solvent at a concentration of 1-10%. By performing the agingstep of the present invention, the formed network structure can be morefirmly formed, and mechanical stability can be enhanced.

In addition, the dried silica aerogel maintains a low thermalconductivity just after drying, but absorbs water in the air due to thehydrophilicity of a silanol group (Si—OH) on the silica surface, so thatthere is a disadvantage in that the nanopore structure is shrunk due tothe condensation reaction of the silanol group, thereby graduallyincreasing the thermal conductivity gradually. Therefore, in order tomaintain a low thermal conductivity, there is a need to modify thesurface of silica aerogel so as to be hydrophobic. Accordingly, asurface modification step for modifying the surface of silica aerogelsurface by using a surface modifier can be additionally performed, andthe surface modification of the present invention can be performed byadding one or more surface modifiers selected from the group consistingof trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS),methyltrimethoxysilane, trimethylethoxysilane, ethyltriethoxysilane,phenyltriethoxysilane, and polydimethylsiloxane, and more specifically,by adding hexamethyldisilazane (HMDS).

Thereafter, a hydrophobic silica aerogel can be produced through adrying process of removing a solvent while maintaining the porestructure of the hydrophobic silica gel, the surface of which has beenmodified. The drying process can be performed by an ambient dryingprocess or a supercritical drying process.

The ambient drying process does not require high pressure reactionconditions and a special high pressure equipment for supercriticaldrying, so that the process thereof is simple and economical. However,since water or an organic solvent evaporates at a high temperature, whencompared with supercritical drying, ambient drying has a problem in thatthe heat insulation performance is sharply reduced due to the occurrenceof the destruction of the pore structure inside a gel. In addition, theabove problem can be further exacerbated when drying is directlyperformed without the substitution with an organic solvent having a lowsurface tension.

In comparison, the drying of the present invention is capable ofmaximizing porosity by implementing supercritical drying, so that theheat insulation performance can be far superior to that of a silica gelproduced by ambient drying.

Apparatus for Producing Silica Aerogel Blanket

In addition, as shown in FIG. 2 and FIG. 3 , the present inventionprovides an apparatus for producing a silica aerogel blanket which iscapable of producing a silica aerogel blanket according to the methodfor producing a silica aerogel blanket of the present invention.

The apparatus for producing a silica aerogel blanket of the presentinvention is characterized by including an apparatus for producing asilica aerogel blanket, the apparatus comprising: an impregnation tankin which a blanket is impregnated with silica sol and a gelationcatalyst;

a blanket supply apparatus connected to one side of the impregnationtank and supplying a blanket;

a silica sol injection apparatus for injecting silica sol into theimpregnation tank such that the supplied blanket is impregnated with thesilica sol;

a gelation catalyst injection apparatus for injecting a gelationcatalyst into the impregnation tank such that the supplied blanket isimpregnated with the gelling catalyst;

an ascending slope connected to the other side of the impregnation tankand transferring the blanket impregnated with the silica sol and thegelation catalyst from the impregnation tank to a moving element; and

a moving element connected to the ascending slope and on which theblanket impregnated with the silica sol and the gelation catalyst isgelled.

Specifically, according to an apparatus according to an embodiment ofthe present invention, silica sol and a gelation catalyst are stored ina separate tank, and the silica sol is injected through a silica solinjection apparatus (2) and the gelation catalyst is injected through agelation catalyst injection apparatus (3), separately. Specifically, thesilica sol and the gelation catalyst are introduced into several flowmeters to be sprayed through nozzles onto a blanket supplied to animpregnation tank (5), and each injection rate is controlled by acontrol device (4) connected to each tank.

Meanwhile, the fibrous blanket is wound in the form of a roll andsupplied to the impregnation tank (5) at a constant rate by a blanketsupply device (1). The sprayed silica sol and the gelation catalyst aremixed with the blanket while being impregnated thereinto in theimpregnation tank (5). The liquid level of the mixed solution of thesilica sol and the gelation catalyst sprayed onto the impregnation tank(5) is maintained to overflow a little over the fibrous blanket, so thatuniform impregnation is achieved. In the impregnation tank (5), one ormore squeeze rollers (6) are additionally present to induce the mixtureand uniform impregnation of the silica sol and the gelation catalystinto the inside of the blanket.

The blanket stays in the impregnation tank (5) for a predeterminedperiod of time such that sufficient and uniform impregnation isachieved, and is transferred along an ascending slope (7), so that anexcessive amount of the mixed solution of the silica sol and thegelation catalyst flows down along the slope into the impregnation tankto prevent excessive impregnation, ensuring an appropriate level ofimpregnation (saturated impregnation).

Thereafter, the transferred from the ascending slope (7) is transferredto a moving element (8), and a gelation reaction occurs on the movingelement (8) to produce a silica wet gel blanket. A scraper (9)additionally present on the moving element (8) adjusts the thickness ofthe blanket, so that the thickness of the silica aerogel blanketprepared in the production apparatus of the present invention can beuniformly controlled.

Although not illustrated in the drawings, after the gelation reaction iscompleted, the silica wet gel blanket can be recovered in the form of amoving element or a roll, and then additionally subjected to aging,surface modification and then drying in a separate container to finallyproduce a silica aerogel blanket.

Hereinafter, examples of the present invention will be described indetail so that those skilled in the art can easily carry out the presentinvention. The present invention can, however, be embodied in manydifferent forms and is not limited to the examples set forth herein.

Example 1

As a silica precursor, 9 kg of hydrolyzed TEOS was mixed with 27 kg ofethanol to prepare 32.5 L of silica sol (Target density (TD) 40 kg/m³).Separately, 40.2 kg of ethanol and 0.35 kg of NH₄OH (30=aqueoussolution) were mixed to prepare a gelation catalyst solution. The silicasol was introduced into an impregnation tank before a gel castingapparatus at a constant flow rate of 1.2 L/min, and a polyester fiber(glass fiber mat) passing at a constant speed was impregnated into theimpregnation tank. The gelation catalyst solution was injected at 0.12L/min onto the sol-impregnated fiber and the impregnation tank. Thefiber mat impregnated with the silica sol and the gelation catalyst inthe impregnation tank was then elevated upward along a slope, and whilepassing over a conveyor belt at a constant speed, gelation was performedthereon. The gelation was performed for 10 minutes, and after thegelation was completed, the gelled fiber mat was stabilized for 10minutes at room temperature (25° C.), and followed by pre-aging in anoven at 70° C. for 50 minutes. The mixture of ethanol and NH₄OH (volumeratio of 98:2) was prepared to be added to a resulting reaction mixturein an amount of 1.6 times of the volume of silica sol, and then agingwas performed in an oven at 70° C. for 1 hour, followed by surfacemodification using hexamethyldisilazane. After the surface modificationwas completed, a silica gel-fiber composite was placed into asupercritical extractor of 7.2 L and CO₂ was continuously injectedthereto at 28° C. and 70 bar for 10 minutes at a rate of 70 L/min.Thereafter, the temperature inside the extractor was raised to 50° C.over 1 hour and 20 minutes, and upon reaching 50° C. and 150 bar, CO₂was continuously injected thereto for 20 minutes at a rate of 5 L/min.At this time, ethanol was recovered through a lower end of a separator.After 20 minutes of resting, supercritical drying was performed bycontinuously injecting CO₂ at a rate of 5 L/min over 20 minutes.Thereafter, CO₂ was vented over 2 hours to produce a silica aerogelblanket.

Examples 2 to 4

A silica aerogel blanket was produced in the same manner as in Example 1except that 32.5 L of silica sol (TD=60 kg/m³, 80 kg/m³, 100 kg/m³) anda gelation catalyst solution were added at 0.06, 0.048, 0.041 L/minrespectively, as shown in Table 1 below.

Comparative Example 1

As a silica precursor, 9.9 kg of hydrolyzed TEOS was mixed with 27 kg ofethanol to prepare 32.5 L of silica sol (Target density (TD) 40 kg/m³).Separately, 4.2 kg of ethanol and 0.35 kg of NH₄OH (30% aqueoussolution) were mixed to prepare a gelation catalyst solution, and theprepared gelation catalyst solution was added with the silica sol.Without an impregnation tank, a polyester fiber (glass fiber mat)passing a conveyor belt at a constant speed was introduced thereto, thatis, onto a gel casting apparatus at a constant flow rate of 1.32 L/minto be impregnated, followed gelation for 10 minutes. After the gelation,a silica aerogel blanket was produced in the same manner as in Example1.

Experimental Example 1: Measurement of Aerogel Content in Blanket andThermal Conductivity

The content of aerogel contained in the silica aerogel blankets producedin Examples 1 to 4 and Comparative Example 1 were measured bysubtracting the initial blanket fiber weight from the weight of theproduced aerogel blanket, and as for thermal conductivity, hightemperature thermal conductivity was measured using GHP 456 of NETZSCHCo. The results are shown in Table 1 below.

TABLE 1 Content of aerogel in Catalyst silica Target injection aerogelThermal density rate blanket conductivity (kg/m³) (L/min) (wt %) (mW/mK)Example 1 40 0.120 30 14.5 Example 2 60 0.060 38 13.9 Example 3 80 0.04845 13.3 Example 4 100 0.041 55 13.0 Comparative 40 0.120 27 18.0 Example1 (Mixed with sol and then injected

Experimental Example 2: Dust Generation Experiment

The silica aerogel blankets produced in Example 1 and ComparativeExample 1 were cut to a size of 600×900 mm², and vibrated for 6 hours at12 Hz to measure the weight change of silica aerogel blanketbefore/after the vibration. The results are shown in Table 2 below.

TABLE 2 Before After Weight Increase/deer vibration vibration changeease rate (g) (g) (g) (%) Example 1 1035 1030 <5 <−0.5% Comparative 10351019 16 −1.5% Example 1

As shown in Table 2, the silica aerogel blanket of Example 1 produced bythe production method of the present invention has a significantly smallamount of dust when compared with that of Comparative Example 1.

This is due to performing impregnation in an impregnation apparatus suchthat the silica sol and the gelation catalyst are uniformly andsufficiently impregnated into the blanket, and allowing the blanket tobe transferred from the impregnation apparatus to the moving elementthrough the ascending slope such that an excessive amount of silica soland gelation catalyst flows down to the bottom of the impregnationapparatus so as to prevent the formation of aerogel formed without afibrous blanket structure.

Experimental Example 3: Scanning Electron Microscope (SEM) Photograph

An SEM photograph of each of the silica aerogel blankets produced inExample 1 and Comparative Example 1 was taken and is shown in FIG. 4 .

As shown in FIG. 4 , the silica aerogel blanket of Example 1 produced bythe production method of the present invention has silica aerogeluniformly combined between the fibrous fiber when compared with that ofComparative Example 1.

Experimental Example 4: Thermal Imaging Camera Photograph

The silica aerogel blankets produced in Example 1 and ComparativeExample 1 were wrapped around a pipe of −175° C., and the thermalimaging camera photographs thereof were taken using FLIR T62101equipment of FLIR Co. The results are shown in FIG. 5 .

As shown in FIG. 5 , the silica aerogel blanket of Example 1 produced bythe production method of the present invention has uniform thermalinsulation performance when compared with that of Comparative Example 1.

Experimental Example 5: Measurement of Pore Size Distribution of Aerogel

The pore size distribution of silica aerogel of silica aerogel blanketsproduced in Example 1 and Comparative Example 1 was measured and theresults are show in FIG. 6 .

As shown in FIG. 6 , the silica aerogel blanket of Example 1 produced bythe production method of the present invention has uniform pore sizedistribution of silica aerogel when compared with that of ComparativeExample 1.

The foregoing description of the present invention has been presentedfor purposes of illustration. It will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention. It istherefore to be understood that the above-described embodiments areillustrative in all aspects and not restrictive.

DESCRIPTION OF SYMBOLS

-   -   1: Blanket supply apparatus    -   2: Silica sol injection apparatus    -   3: Gelation catalyst injection apparatus    -   4: Control unit    -   5: Impregnation tank    -   6: Squeeze roller    -   7: Ascending slope    -   8: Moving element    -   9: Scraper

1. An apparatus for producing a silica aerogel blanket, the apparatuscomprising: an impregnation tank having a first side and an oppositesecond side in which a blanket is impregnated with silica sol and agelation catalyst; a blanket supply apparatus connected to the firstside of the impregnation tank that supplies a blanket; a silica solinjector for injecting silica sol into the impregnation tank such thatthe supplied blanket is impregnated with the silica sol; a gelationcatalyst injector for injecting a gelation catalyst into theimpregnation tank such that the supplied blanket is impregnated with thegelling catalyst; an ascending slope connected to the second side of theimpregnation tank; and a moving element connected to the ascending slopeand on which the blanket impregnated with the silica sol and thegelation catalyst is gelled, the ascending slope transferring theblanket impregnated with the silica sol and the gelation catalyst fromthe impregnation tank to the moving element.
 2. The apparatus of claim1, wherein the moving element is located above the impregnation tank. 3.The apparatus of claim 1, wherein the silica sol injector and thegelation catalyst injector each further comprise a separate controldevice for controlling an injection rate from each injector.
 4. Theapparatus of claim 1, wherein the silica sol injector and the gelationcatalyst injector are located above or below the impregnation tank. 5.The apparatus of claim 1, wherein the silica sol injector and thegelation catalyst injector are respectively one or more.
 6. Theapparatus of claim 1, wherein the impregnation tank further comprises asqueeze roller for inducing the impregnation of silica sol and agelation catalyst into the inside of a blanket.
 7. The apparatus ofclaim 1, wherein the angle of the ascending slope is greater than 0° toless than 180°.
 8. The apparatus of claim 1, wherein the moving elementfurther comprises one or more scrapers.
 9. The apparatus of claim 5,further comprising a flow meter independently attached to each nozzle.